The present invention relates to the circuit configuration of a probe for a NMR (nuclear magnetic resonance) apparatus.
Nuclear magnetic resonance (NMR) spectroscopy is expected as one of effective tools for performing the structural analysis of macromolecular organic substances such as proteins in leading-edge life science and pharmaceutical production fields.
Since NMR is not so high in the measurement sensitivity, its high-sensitivity implementation can be pointed out as one of the problems concerned with NMR. Also, in order to analyze the structure of a more complicated molecule, it is becoming more and more required to enhance resolution of the resultant spectrum. In the history of NMR, the sensitivity and the resolution have been enhanced mainly by enhancing intensity of the static magnetic field.
As the other methods of enhancing the sensitivity, there exist methods of enhancing the probe performance. As one of them, there has been known a method of enhancing Q value of a probe coil. This Q value, which means the Q value in an electrical resonance, is given by Q=ωCL/r in a simple parallel resonance circuit. Here, the simple parallel resonance circuit includes a coil having inductance L and series resistance r, and a capacitor having capacitance C.
Adjustment of the resonant frequency ωC is performed using a variable capacitor. In the measurement of radio-frequency waves of a few tens of MHz or more, impedance matching is absolutely necessary for observing the signal effectively. The impedance matching is performed by a tuning circuit simultaneously with adjustment of the tuning. Here, the tuning circuit includes two or more capacitors as are illustrated in FIG. 6.
As another method of enhancing the probe performance, there exists a method disclosed in U.S. Pat. No. 6,121,776. By cooling the probe coil manufactured with a superconducting material, this method allows low-temperature operation of the probe, coil. Namely, thermal noise is reduced by cooling the detection coil of the probe, and the Q value is enhanced by cooling resistant substances of the electric wires. As a result of this, the sensitivity is enhanced.
It depends largely on the probe performance whether or not the high resolution and high S/N (: signal-to-noise) ratio requested in the high-sensitivity measurement can be accomplished. In particular, the detection coil of the probe becomes the most influential factor to hinder and disturb an exceedingly uniform magnetic field of about 0.1 ppb which is going to be generated in a sample space. This is because the detection coil exists in close vicinity to the sample.
As described above, manufacturing the detection coil with the superconducting material makes it possible to implement the high Q value. Meanwhile, manufacturing the detection coil with a normal conducting material allows implementation of the magnetization adjustment. In the latter case, however, it is impossible to accomplish a Q value which is almost comparable to the Q value implemented by the superconducting detection coil, even if the normal conducting detection coil is cooled down to the low temperature.